1. Field of the Invention
The present invention relates to a rotation-angular-position detecting apparatus for detecting the angular position of the rotation of a rotor.
2. Description of Background Art
To control the fuel injection timing for injecting fuel into an internal combustion engine by using an injector and ignition timing to discharge sparks to an ignition plug, the angular position of the rotation of a crank shaft of the engine is detected by using a rotation-angular-position detecting apparatus. A detected angular position of the rotation is used for setting this kind of timing. The angular position of the rotation is represented by a number called a stage. A reference angular position of the rotation is referred to as stage 0 as is disclosed in Japanese Patent Laid-open No. Sho 61-277845.
In the conventional rotation-angular-position detecting apparatus, 2 disc-shaped rotors are provided. The first rotor is rotated in a rotation interlocked with the rotation of a crank shaft. On the circumference of the first rotor, a plurality of detection members to be detected, like protrusions, are formed at equal intervals. The second rotor is rotated at a speed half that of the rotation of the crank shaft. On the circumference of the second rotor, a single detection piece to be detected is formed at a location corresponding to a reference rotation angular position. A first pickup is provided at a position in close proximity to a rotational locus of the plurality of detection members on the first rotor. The first pickup generates a first detection signal when sensing the proximity of any one of the detection members. On the other hand, a second pickup is provided at a position in close proximity to a rotational locus of the detection piece on the second rotor. The second pickup generates a second detection signal when sensing the proximity of the detection piece. A first detection signal generated by the first pickup right after a point in time when the second pickup generates a second detection signal is regarded as a signal indicating stage 0. Then, the number of first detection signals generated thereafter is counted and a stage of the rotation angular position is determined from the count value.
In the conventional rotation-angular-position detecting apparatus, however, it is not until a second detection signal has been generated by the second pickup to indicate the reference rotation angular position that the rotation angular position can be confirmed. For example, there is thus a case in which the second detection signal is not generated until the first rotor reaches a location in close proximity to an angular position of 720 degrees since the start of the rotations of the first and second rotors. In such a case, there is raised a problem regarding the long time for confirmation of an angular position of the rotation.